Preparation method of rubber composition for tire and production method of tire

ABSTRACT

A preparation method of a rubber composition for a tire assures that good processability can be obtained even if a silane coupling agent having a mercapto group is blended. The preparation method of a rubber composition for a tire is characterized by initiating kneading of a rubber component and a compound represented by the following formula (1) before kneading the rubber component and a silane coupling agent having a mercapto group. 
     
       
         
         
             
             
         
       
     
     (Wherein each of R 1  to R 4  independently represents a straight-chain or branched chain alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 5 to 12 carbon atoms.)

TECHNICAL FIELD

The present disclosure relates to a preparation method of a rubbercomposition for a tire and a production method of a tire.

BACKGROUND OF THE INVENTION

Recently, in the light of resources saving, energy saving and inaddition, protection of environment, a strong demand for reduction ofexhausted carbon dioxide is increasing, and various countermeasures suchas weight saving of a vehicle and use of electric energy have beenconsidered. Accordingly, it is demanded to enhance fuel efficiency bydecreasing rolling resistance of a tire for a vehicle, and alsoimprovement of performances such as durability is desired.

For example, there are known, as a method for decreasing rollingresistance, techniques such as blending of silica, decrease in an amountof a filler, use of a filler having less reinforcing property. However,there is a tendency that a mechanical strength of a rubber decreases andvarious performances are degraded.

In JP 2009-120819 A, use of a silane coupling agent having a highlyreactive mercapto group (mercapto silane coupling agent) for the purposeof improving performance such as fuel efficiency has been considered.However, in a mercapto silane coupling agent, good fuel efficiency, wetgrip performance and abrasion resistance are obtained while since themercapto silane coupling agent has high reactivity, there is a concernthat gelation occurs during kneading with a rubber component andprocessability is lowered.

Meanwhile, JP 2012-046602 A describes that in a rubber composition for abase tread which enables fuel efficiency, elongation at break anddurability to be improved in good balance while good steering stabilityand processability (extrusion processability) are maintained even if anamount of zinc oxide is decreased, crosslinking of polymers can be madeuniformly by blending a specific zinc dithiophosphate.

SUMMARY OF THE INVENTION

However, in JP 2012-046602 A, only a role of a crosslinking assistant isdescribed, and the silane coupling agent having a mercapto group and thespecific zinc dithiophosphate are kneaded in the same kneading step, andthere is a room for improvement with respect to processability.

An object of the present disclosure is to provide a preparation methodof a rubber composition for a tire which assures that goodprocessability can be obtained even if a silane coupling agent having amercapto group is blended, and a production method of a tire.

The present inventors have made intensive studies and as a result, havefound that in a method of preparing a rubber composition for a tire byblending a silane coupling agent having a mercapto group, processabilityof an unvulcanized rubber can be improved and the above-mentionedproblem can be solved by initiating kneading of a rubber component and acompound represented by the following formula (1) before kneading therubber component and the silane coupling agent having a mercapto group.The present inventors have made further studies and have completed thepresent disclosure.

Namely, the present disclosure relates to:

[1] a method of preparing a rubber composition for a tire comprisinginitiating kneading of a rubber component and a compound represented bythe following formula (1) before kneading the rubber component and asilane coupling agent having a mercapto group:

wherein each of R¹ to R⁴ independently represents a straight-chain orbranched chain alkyl group having 1 to 18 carbon atoms or a cycloalkylgroup having 5 to 12 carbon atoms,[2] the preparation method of the above [1], wherein the rubbercomponent comprises not less than 50% by mass, preferably not less than60% by mass, more preferably not less than 70% by mass of a diene rubberhaving a styrene content of 25 to 50% by mass, preferably 28 to 47% bymass, more preferably 31 to 44% by mass and an amount of a vinyl bond of10 to 35 mole %, preferably 12 to 33 mole %, more preferably 14 to 31mole %,[3] the preparation method of the above [2], wherein the above-mentionedstyrene content is not less than 2 times, preferably not less than 2.2times the amount of a vinyl bond,[4] the preparation method of any of the above [1] to [3], wherein thesilane coupling agent having a mercapto group is a compound representedby the following formula (2) and/or a compound comprising a bonding unitA represented by the following formula (3) and a bonding unit Brepresented by the following formula (4).

wherein R¹⁰¹ to R¹⁰³ represent a straight-chain or branched chain alkylgroup having 1 to 12 carbon atoms, a straight-chain or branched chainalkoxy group having 1 to 12 carbon atoms, or a group represented by—O—(R¹¹¹—O)_(z)—R¹¹² (z R¹¹¹s represent straight-chain or branched chaindivalent hydrocarbon groups having 1 to 30 carbon atoms, z R¹¹¹s may bethe same or different, R¹¹² represents a straight-chain or branchedchain alkyl group having 1 to 30 carbon atoms, a straight-chain orbranched chain alkenyl group having 2 to 30 carbon atoms, an aryl grouphaving 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbonatoms, z represents an integer of 1 to 30), R¹⁰¹ to R¹⁰³ may be the sameor different, and R¹⁰⁴ represents a straight-chain or branched chainalkylene group having 1 to 6 carbon atoms,

wherein x is an integer of 0 or more, y is an integer of 1 or more, R²⁰¹represents a hydrogen atom, a halogen atom, a straight-chain or branchedchain alkyl group having 1 to 30 carbon atoms, a straight-chain orbranched chain alkenyl group having 2 to 30 carbon atoms, astraight-chain or branched chain alkynyl group having 2 to 30 carbonatoms, or the above alkyl group in which a terminal hydrogen atom hasbeen replaced with a hydroxyl group or a carboxyl group, R²⁰² representsa straight-chain or branched chain alkylene group having 1 to 30 carbonatoms, a straight-chain or branched chain alkenylene group having 2 to30 carbon atoms, or a straight-chain or branched chain alkynylene grouphaving 2 to 30 carbon atoms, and a ring structure may be formed withR²⁰¹ and R²⁰²,[5] a method of producing a tire comprising a step of forming a tiremember from the rubber composition for tire obtained by the preparationmethod of any of the above [1] to [4] and forming a green tire bycombining the tire member with other tire members, and a vulcanizationstep of vulcanizing the green tire obtained in the forming step,[6] a rubber composition for a tire comprising a rubber component, asilane coupling agent having a mercapto group and a compound representedby the following formula (1), which is prepared by kneading the silanecoupling agent having a mercapto group with the rubber component withwhich the compound represented by the following formula (1) is kneaded.

wherein each of R¹ to R⁴ independently represents a straight-chain orbranched chain alkyl group having 1 to 18 carbon atoms or a cycloalkylgroup having 5 to 12 carbon atoms.

According to the method of preparing a rubber composition for a tire ofthe present disclosure, which is characterized in that kneading of arubber component with a compound represented by the above-mentionedformula (1) is initiated before kneading of the rubber component with asilane coupling agent having a mercapto group, a rubber compositionassuring that deterioration of a rubber sheet is inhibited andprocessability is improved can be prepared.

DETAILED DESCRIPTION

The method of preparing a rubber composition for tire of the presentdisclosure is characterized in that kneading of a rubber component witha specific compound represented by the formula (1) is initiated beforekneading of the rubber component with a silane coupling agent having amercapto group. In a composition comprising a rubber component andsilica, by use of a silane coupling agent having a mercapto group, itcan be expected that fuel efficiency and wet grip performance can beenhanced in good balance and abrasion resistance can be improved.Meanwhile, there is a problem with processability such as deteriorationof a rubber sheet at the time of mixing, and it is considered a reasontherefor is such that the mercapto group of the silane coupling agent iseasily subject to radicalization at the time of mixing and is bonded toa polymer, resulting in gelation. According to the feature of thepresent disclosure such that kneading of a rubber component with acompound represented by the formula (1) is initiated before kneading ofthe rubber component with a silane coupling agent having a mercaptogroup, even in the case of using a silane coupling agent having amercapto group, deterioration of a rubber sheet can be prevented andprocess capability can be improved remarkably. This effect is consideredto be such that the radicalized mercapto group of the silane couplingagent reacts with a —S—Zn— structure of the compound represented by theformula (1) before reaction with the rubber component to form a —S—S—bond (namely a radical derived from the mercapto group is captured bythe compound represented by the formula (1)), thereby loweringreactivity of the silane coupling agent with the rubber component andenabling gelation to be prevented, and furthermore, when the temperaturebecomes high during the vulcanization, this disulfide bond is cut andreacts with the rubber component, thereby being capable of fulfilling afunction as a silane coupling agent. Here, since reactivity of thesilane coupling agent having a mercapto group is very high, in thepresent disclosure, the compound represented by the formula (1) iskneaded with the rubber component before kneading the silane couplingagent having a mercapto group with the rubber component but notcoincidently with the kneading of the silane coupling agent having amercapto group, so that radicals can be captured efficiently from thetime when radicalization of the silane coupling agent having a mercaptogroup begins.

In the present disclosure, the compound represented by the formula (1)is as follows.

wherein each of R¹ to R⁴ independently represents a straight-chain orbranched chain alkyl group having 1 to 18 carbon atoms or a cycloalkylgroup having 5 to 12 carbon atoms.

In the above formula (1), each of R¹ to R⁴ independently represents astraight-chain or branched chain alkyl group having 1 to 18 carbon atomsor a cycloalkyl group having 5 to 12 carbon atoms. Examples of thestraight-chain or branched chain alkyl group represented by R¹ to R⁴include methyl, ethyl, n-propyl, iso-propyl, n-butyl, 4-methylpentyl,2-ethylhexyl, octyl, octadecyl and the like, and examples of thecycloalkyl group include cyclopentyl, cyclohexyl, cyclooctyl and thelike. Among these, from the viewpoint of easy dispersion in a rubbercomponent and easy preparation, R¹ to R⁴ are preferably straight-chainor branched chain alkyl groups having 2 to 18 carbon atoms and n-butyl,n-propyl, iso-propyl and n-octyl are more preferable.

For example, TP-50 and ZBOP-50 available from Rhein Chemie and compoundsanalogous thereto (for example, those in which each of R¹ to R⁴ isn-propyl, iso-propyl or n-octyl) can be used as the compound representedby the formula (1).

A content of the compound represented by the formula (1) (a content ofactive ingredient) is preferably not less than 0.1 part by mass, morepreferably not less than 0.2 part by mass, further preferably not lessthan 0.3 part by mass based on 100 parts by mass of silica. When thecontent of the compound of the formula (1) is not less than 0.1 part bymass, there is a tendency that an unvulcanized rubber sheet after thekneading becomes significantly smooth. Further, the content of thecompound of the formula (1) is preferably not more than 5 parts by mass,more preferably not more than 3 parts by mass based on 100 parts by massof silica. When the content of the compound of the formula (1) is notmore than 5 parts by mass, there is a tendency that deterioration of abreaking strength and abrasion resistance does not occur.

The content of the compound of the formula (1) is preferably not lessthan 1 part by mass, more preferably not less than 3 parts by mass basedon 100 parts by mass of the silane coupling agent having a mercaptogroup. When the content of the compound of the formula (1) is not lessthan 1 part by mass, there is a tendency that an unvulcanized rubbersheet after the kneading becomes significantly smooth. Further, thecontent of the compound of the formula (1) is preferably not more than100 parts by mass, more preferably not more than 50 parts by mass basedon 100 parts by mass of the silane coupling agent having a mercaptogroup. When the content of the compound of the formula (1) is not morethan 100 parts by mass, there is a tendency that deterioration of abreaking strength and abrasion resistance does not occur.

In the present disclosure, the silane coupling agent having a mercaptogroup is a compound represented by the following formula (2) and/or acompound comprising a bonding unit A represented by the followingformula (3) and a bonding unit B represented by the following formula(4).

wherein R¹⁰¹ to R¹⁰³ represent a straight-chain or branched chain alkylgroup having 1 to 12 carbon atoms, a straight-chain or branched chainalkoxy group having 1 to 12 carbon atoms, or a group represented by—O—(R¹¹¹—O)_(z)—R¹¹² (z R¹¹¹s represent straight-chain or branched chaindivalent hydrocarbon groups having 1 to 30 carbon atoms, z R¹¹¹s may bethe same or different, R¹¹² represents a straight-chain or branchedchain alkyl group having 1 to 30 carbon atoms, a straight-chain orbranched chain alkenyl group having 2 to 30 carbon atoms, an aryl grouphaving 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbonatoms, z represents an integer of 1 to 30), R¹⁰¹ to R¹⁰³ may be the sameor different, and R¹⁰⁴ represents a straight-chain or branched chainalkylene group having 1 to 6 carbon atoms,

wherein x is an integer of 0 or more, y is an integer of 1 or more, R²⁰¹represents a hydrogen atom, a halogen atom, a straight-chain or branchedchain alkyl group having 1 to 30 carbon atoms, a straight-chain orbranched chain alkenyl group having 2 to 30 carbon atoms, astraight-chain or branched chain alkynyl group having 2 to 30 carbonatoms, or the above alkyl group in which a terminal hydrogen atom hasbeen replaced with a hydroxyl group or a carboxyl group, R²⁰² representsa straight-chain or branched chain alkylene group having 1 to 30 carbonatoms, a straight-chain or branched chain alkenylene group having 2 to30 carbon atoms, or a straight-chain or branched chain alkynylene grouphaving 2 to 30 carbon atoms, and a ring structure may be formed withR²⁰¹ and R²⁰².

The compound represented by the above formula (2) is described below.

R¹⁰¹ to R¹⁰³ represent a straight-chain or branched chain alkyl grouphaving 1 to 12 carbon atoms, a straight-chain or branched chain alkoxygroup having 1 to 12 carbon atoms, or a group represented by—O—(R¹¹¹—O)_(z)—R¹¹². From the viewpoint that the effect of the presentdisclosure can be obtained satisfactorily, it is preferable that atleast one of R¹⁰¹ to R¹⁰³ is a group represented by—O—(R¹¹¹—O)_(z)—R¹¹², and it is more preferable that two of R¹⁰¹ to R¹⁰³are groups represented by —O—(R¹¹¹—O)_(z)—R¹¹², and the remaining one isa straight-chain or branched chain alkoxy group having 1 to 12 carbonatoms.

Examples of the straight-chain or branched chain alkyl group having 1 to12 carbon atoms (preferably 1 to 5 carbon atoms) of R¹⁰¹ to R¹⁰³ includemethyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, sec-butyl,tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl and thelike.

Examples of the straight-chain or branched chain alkoxy group having 1to 12 carbon atoms (preferably 1 to 5 carbon atoms) of R¹⁰¹ to R¹⁰³include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, iso-butoxy,sec-butoxy, tert-butoxy, pentyloxy, hexyloxy, heptyloxy,2-ethylhexyloxy, octyloxy, nonyloxy, and the like.

In —O—(R¹¹¹—O)_(z)—R¹¹² of R¹⁰¹ to R¹⁰³, R¹¹¹ represents astraight-chain or branched chain divalent hydrocarbon group having 1 to30 carbon atoms (preferably 1 to 15 carbon atoms, more preferably 1 to 3carbon atoms). Examples of the hydrocarbon group include astraight-chain or branched chain alkylene group having 1 to 30 carbonatoms, a straight-chain or branched chain alkenylene group having 2 to30 carbon atoms, a straight-chain or branched chain alkynylene grouphaving 2 to 30 carbon atoms, an arylene group having 6 to 30 carbonatoms, and the like. Among these, a straight-chain or branched chainalkylene group having 1 to 30 carbon atoms is preferable.

Examples of the straight-chain or branched chain alkylene group having 1to 30 carbon atoms (preferably 1 to 15 carbon atoms, more preferably 1to 3 carbon atoms) of R¹¹¹ include methylene, ethylene, propylene,butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene,undecylene, dodecylene, tridecylene, tetradecylene, pentadecylene,hexadecylene, heptadecylene, octadecylene, and the like.

Examples of the straight-chain or branched chain alkenylene group having2 to 30 carbon atoms (preferably 2 to 15 carbon atoms, more preferably 2or 3 carbon atoms) of R¹¹¹ include vinylene, 1-propenylene,2-propenylene, 1-butenylene, 2-butenylene, 1-pentenylene, 2-pentenylene,1-hexenylene, 2-hexenylene, 1-octenylene, and the like.

Examples of the straight-chain or branched chain alkynylene group having2 to 30 carbon atoms (preferably 2 to 15 carbon atoms, more preferably 2or 3 carbon atoms) of R¹¹¹ include ethynylene, propynylene, butynylene,pentynylene, hexynylene, heptynylene, octynylene, nonynylene,decynylene, undecynylene, dodecynylene, and the like.

Examples of the arylene group having 6 to 30 carbon atoms (preferably 6to 15 carbon atoms) of R¹¹¹ include phenylene, tolylene, xylylene,naphthylene, and the like.

The z is an integer of 1 to 30, preferably 2 to 20, more preferably 3 to7, further preferably 5 or 6.

R¹¹² represents a straight-chain or branched chain alkyl group having 1to 30 carbon atoms, a straight-chain or branched chain alkenyl grouphaving 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atomsor an aralkyl group having 7 to 30 carbon atoms. Among these, thestraight-chain or branched chain alkyl group having 1 to 30 carbon atomsis preferable.

Examples of the straight-chain or branched chain alkyl group having 1 to30 carbon atoms (preferably 3 to 25 carbon atoms, more preferably 10 to15 carbon atoms) of R¹¹² include methyl, ethyl, n-propyl, isopropyl,n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl,2-ethylhexyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl,tetradecyl, pentadecyl, octadecyl, and the like.

Examples of the straight-chain or branched chain alkenyl group having 2to 30 carbon atoms (preferably 3 to 25 carbon atoms, more preferably 10to 15 carbon atoms) of R¹¹² include vinyl, 1-propenyl, 2-propenyl,1-butenyl, 2-butenyl, 1-pentenyl, 2-pentenyl, 1-hexenyl, 2-hexenyl,1-octenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl,pentadecenyl, octadecenyl, and the like.

Examples of the aryl group having 6 to 30 carbon atoms (preferably 10 to20 carbon atoms) of R¹¹² include phenyl, tolyl, xylyl, naphthyl,biphenyl, and the like.

Examples of the aralkyl group having 7 to 30 carbon atoms (preferably 10to 20 carbon atoms) of R¹¹² include benzyl, phenethyl, and the like.

Examples of the group represented by —O—(R¹¹¹—O)_(z)—R¹¹² include—O—(C₂H₄—O)₅—C₁₁H₂₃, —O—(C₂H₄—O)₅—C₁₂H₂₅, —O—(C₂H₄—O)₅—C₁₃H₂₇,—O—(C₂H₄—O)₅—C₁₄H₂₉, —O—(C₂H₄—O)₅—C₁₅H₃₁, —O—(C₂H₄—O)₃—C₁₃H₂₇,—O—(C₂H₄—O)₄—C₁₃H₂₇, —O—(C₂H₄—O)₆—C₁₃H₂₇, —O—(C₂H₄—O)₇—C₁₃H₂₇, and thelike. Among these, —O—(C₂H₄—O)₅—C₁₁H₂₃, —O—(C₂H₄—O)₅—C₁₃H₂₇,—O—(C₂H₄—O)₅—C₁₅H₃₁ and —O—(C₂H₄—O)₆—C₁₃H₂₇ are preferable.

Examples of the straight-chain or branched chain alkylene group having 1to 6 carbon atoms (preferably 1 to 5 carbon atoms) of R¹⁰⁴ includegroups analogous to the straight-chain or branched chain alkylene grouphaving 1 to 30 carbon atoms of R¹¹¹.

Examples of the compound represented by the above-mentioned formula (2)include 3-mercaptopropyltrimethoxysilane,3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane,2-mercaptoethyltriethoxysilane, a compound represented by the followingformula (Si363 available from Evonik-Degussa GmbH), and the like, andthe compound represented by the following formula can be used suitably.These compounds may be used alone or may be used in combination of twoor more thereof.

Next, the compound comprising the bonding unit A represented by thementioned formula (3) and the bonding unit B represented by thementioned formula (4) will be described.

The compound comprising the bonding unit A represented by the mentionedformula (3) and the bonding unit B represented by the mentioned formula(4) assures that increase in a viscosity during processing is inhibitedas compared with a polysulfide silane such asbis-(3-triethoxysilylpropyl)tetrasulfide. It can be considered that thereason therefor is that since a sulfide moiety of the bonding unit A isa C—S—C bond, the compound is thermally stable as compared with atetrasulfide and a disulfide and thus increase in a Mooney viscosity issmall.

Further, as compared with a mercapto silane such as3-mercaptopropyltrimethoxysilane, reduction of a scorch time isinhibited. It can be considered that the reason therefor is that whilethe bonding unit B has a mercapto silane structure, a —C₇H₁₅ moiety ofthe bonding unit A covers a —SH group of the bonding unit B, and thusthe compound is hardly reacted with a polymer and scorching is hardlycaused.

From the viewpoint that an effect of inhibiting increase in viscosityduring the processing and an effect of inhibiting reduction of ascorching time can be enhanced, in the silane coupling agent having theabove-mentioned structure, the content of the bonding unit A ispreferably not less than 30 mole %, more preferably not less than 50mole %, and preferably not more than 99 mole %, more preferably not morethan 90 mole %. On the other hand, the content of the bonding unit B ispreferably not less than 1 mole %, more preferably not less than 5 mole%, further preferably not less than 10 mole %, and preferably not morethan 70 mole %, more preferably not more than 65 mole %, furtherpreferably not more than 55 mole %. Further, the total content of thebonding unit A and the bonding unit B is preferably not less than 95mole %, more preferably not less than 98 mole %, particularly preferably100 mole %. The contents of the bonding unit A and the bonding unit Binclude the contents of the bonding unit A and the bonding unit B beingpresent at a terminal of the silane coupling agent. A mode of thebonding unit A and the bonding unit B being present at a terminal of thesilane coupling agent is not limited particularly, as long as it forms aunit corresponding to the formulas (3) and (4) which represent thebonding unit A and the bonding unit B, respectively.

Examples of a halogen atom of R²⁰¹ include chlorine atom, bromine atom,fluorine atom and the like.

Examples of the straight-chain or branched chain alkyl group having 1 to30 carbon atoms of R²⁰¹ include methyl, ethyl, n-propyl, isopropyl,n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl,2-ethylhexyl, octyl, nonyl, decyl and the like. The number of carbonatoms of the alkyl group is preferably from 1 to 12.

Examples of the straight-chain or branched chain alkenyl group having 2to 30 carbon atoms of R²⁰¹ include vinyl, 1-propenyl, 2-propenyl,1-butenyl, 2-butenyl, 1-pentenyl, 2-pentenyl, 1-hexenyl, 2-hexenyl,1-octenyl, and the like. The number of carbon atoms of the alkenyl groupis preferably from 2 to 12.

Examples of the straight-chain or branched chain alkynyl group having 2to 30 carbon atoms of R²⁰¹ include ethynyl, propynyl, butynyl, pentynyl,hexynyl, heptynyl, octynyl, nonynyl, decynyl, undecynyl, dodecynyl, andthe like. The number of carbon atoms of the alkynyl group is preferablyfrom 2 to 12.

Examples of the straight-chain or branched chain alkylene group having 1to 30 carbon atoms of R²⁰² include ethylene, propylene, butylene,pentylene, hexylene, heptylene, octylene, nonylene, decylene,undecylene, dodecylene, tridecylene, tetradecylene, pentadecylene,hexadecylene, heptadecylene, octadecylene, and the like. The number ofcarbon atoms of the alkylene group is preferably from 1 to 12.

Examples of the straight-chain or branched chain alkenylene group having2 to 30 carbon atoms of R²⁰² include vinylene, 1-propenylene,2-propenylene, 1-butenylene, 2-butenylene, 1-pentenylene, 2-pentenylene,1-hexenylene, 2-hexenylene, 1-octenylene, and the like. The number ofcarbon atoms of the alkenylene group is preferably from 2 to 12.

Examples of the straight-chain or branched chain alkynylene group having2 to 30 carbon atoms of R²⁰² include ethynylene, propynylene,butynylene, pentynylene, hexynylene, heptynylene, octynylene,nonynylene, decynylene, undecynylene, dodecynylene, and the like. Thenumber of carbon atoms of the alkynylene group is preferably from 2 to12.

In the compound comprising the bonding unit A represented by thementioned formula (3) and the bonding unit B represented by thementioned formula (4), the total (x+y) of the recurring bonding units A(x) and the recurring bonding units B (y) is preferably from 3 to 300.When the total is within this range, since —C₇H₁₅ of the bonding unit Acovers the mercapto silane of the bonding unit B, reduction of a scorchtime can be inhibited and good reactivity with silica and the rubbercomponent can be secured.

For example, NXT-Z30, NXT-Z45, NXT-Z60 and the like manufactured byMomentive can be used as the compound comprising the bonding unit Arepresented by the mentioned formula (3) and the bonding unit Brepresented by the mentioned formula (4). These may be used alone or maybe used in combination of two or more thereof.

A content of the silane coupling agent having a mercapto group ispreferably not less than 0.5 part by mass, more preferably not less than1 part by mass, further preferably not less than 2 parts by mass,particularly preferably not less than 4 parts by mass based on 100 partsby mass of silica. When the content is less than 0.5 part by mass, asufficient effect of improving fuel efficiency may not be obtained. Onthe other hand, the content is preferably not more than 20 parts bymass, more preferably not more than 12 parts by mass, further preferablynot more than 10 parts by mass, particularly preferably not more than 9parts by mass. When the content is more than 20 parts by mass, there isa tendency that a rubber strength and abrasion resistance decrease.

In the present disclosure, the rubber composition may comprise anothersilane coupling agent in addition to the above-mentioned silane couplingagent having a mercapto group. Examples of another silane coupling agentinclude 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-trimethoxysilylpropylbenzothiazole tetrasulfide,3-triethoxysilylpropylbenzothiazolyl tetrasulfide,3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropylmethacrylate monosulfide, bis(3-triethoxysilylpropyl)tetrasulfide,bis(3-triethoxysilylpropyl)trisulfide,bis(3-triethoxysilylpropyl)disulfide,bis(2-triethoxysilylethyl)tetrasulfide,bis(3-trimethoxysilylpropyl)tetrasulfide,bis(2-trimethoxysilylethyl)tetrasulfide,bis(3-diethoxymethylsilylpropyl)tetrasulfide,3-mercaptopropyldimethoxymethylsilane,dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,dimethoxymethylsilylpropylbenzothiazole tetrasulfide, and the like.

In the present disclosure, the rubber component is not limitedparticularly, and rubber components which have been used for rubbercompositions for tire can be used. Examples thereof include diene rubbercomponents such as isoprene rubber including natural rubber andpolyisoprene rubber (IR), butadiene rubber (BR), styrene-butadienerubber (SBR), styrene-isoprene-butadiene rubber (SIBR), chloroprenerubber (CR) and acrylonitrile-butadiene rubber (NBR), and butyl rubbers.These rubber components can be used alone or can be used in combinationof two or more thereof. In particular, it is preferable that the rubbercomposition comprises one or more rubber components comprising aconjugated diene compound, and it is preferable that the rubbercomposition comprises SBR and BR from the viewpoint of a balance of fuelefficiency, abrasion resistance, durability and wet grip performance.

Further, in the present disclosure, it is preferable to use a dienerubber having a styrene content of 25 to 50% by mass and an amount ofvinyl bond of 10 to 35 mole % as the diene rubber, for the reason thatwet skid performance, dry grip performance and fuel efficiency can beobtained in good balance. Examples of a diene rubber comprising styreneand vinyl include SBR and SIBR.

A styrene content of the diene rubber is preferably not less than 25% bymass, more preferably not less than 28% by mass, further preferably notless than 31% by mass, from the viewpoint of grip performance. When thestyrene content is too large, styrene groups become in proximity to eachother, a polymer becomes too hard and crosslinking becomes non-uniform,which may deteriorate blowing property during running at hightemperature, and further there is a tendency that since temperaturedependency of the performances is increased and the performances can bechanged largely with respect to a temperature change, stable gripperformance cannot be obtained at a middle and latter stage of running.Therefore, the styrene content is preferably not more than 50% by mass,more preferably not more than 47% by mass, further preferably not morethan 44% by mass. Herein, the styrene content of the diene rubber iscalculated in accordance with ¹H-NMR measurement.

An amount of vinyl bond of the diene rubber is preferably not less than10 mole %, more preferably not less than 12 mole %, further preferablynot less than 14 mole %, for security of reactivity with silica and fromthe viewpoint of a rubber strength and abrasion resistance. On the otherhand, for prevention of increase in temperature dependency and from theviewpoint of grip performance, EB (durability) and abrasion resistance,the amount of vinyl bond of the diene rubber is preferably not more than35 mole %, more preferably not more than 33 mole %, further preferablynot more than 31 mole %. Herein, the amount of vinyl bond of SBR (anamount of 1,2-bond butadiene unit) can be determined by an infraredabsorption spectrum analysis method.

When the rubber component comprises a diene rubber having a styrenecontent of 25 to 50% by mass and an amount of vinyl bond of 10 to 35mole %, the content of the diene rubber in the rubber component ispreferably not less than 50% by mass, more preferably not less than 60%by mass, further preferably not less than 70% by mass. When the contentof the diene rubber is not less than 50% by mass, there is a tendencythat change of the performances within a high temperature range can beinhibited and higher grip performance and blowing property can beexhibited. On the other hand, the content of the diene rubber ispreferably not more than 90% by mass, more preferably not more than 85%by mass, further preferably not more than 80% by mass, from theviewpoint of abrasion resistance, grip performance and fuel efficiency.

Furthermore, in the above-mentioned diene rubber, the styrene content ispreferably not less than 2 times, more preferably not less than 2.2times the amount of a vinyl bond in the light of compatibility of wetskid performance with fuel efficiency. While an upper limit thereof isnot limited particularly, the styrene content of the diene rubber ispreferably not more than 3.0 times the amount of a vinyl bond. When thestyrene content exceeds 3.0 times the amount of a vinyl bond, there is atendency that a glass transition temperature increases excessively, andfuel efficiency and low-temperature characteristic are loweredsignificantly.

The SBR is not limited particularly, and there are anemulsion-polymerized SBR (E-SBR), a solution-polymerized SBR (S-SBR) andthe like. The SBR may be oil-extended or may not be oil-extended.Further, a terminal-modified S-SBR and a main-chain-modified S-SBR,having enhanced interaction with a filler are also usable. Furthermore,SBRs obtained by hydrogenation of these SBRs (hydrogenated SBR) can alsobe used. These SBRs may be used alone or may be used in combination oftwo or more thereof.

The BR is not limited particularly, and for example, there can be usedBR having a cis content of not less than 95% (high-cis BR), rare earthbutadiene rubber synthesized using a rare-earth element catalyst (rareearth BR), BR having syndiotactic polybutadiene crystal (SPB-containingBR) and modified BR which are used generally in the tire industry. Amongthese, it is preferable to use high-cis BR from a point of excellentabrasion resistance.

When the BR is compounded in the rubber component, a content thereof ispreferably not less than 5% by mass, more preferably not less than 10%by mass. When the content of BR is less than 5% by mass, there is atendency that it is difficult to obtain an effect of enhancing abrasionresistance. On the other hand, the content of BR is preferably not morethan 35% by mass, more preferably not more than 25% by mass. When thecontent of BR exceeds 35% by mass, there is a tendency that dry gripperformance is lowered remarkably and wet grip performance is loweredremarkably.

In the present disclosure, silica is used. By compounding silica, fuelefficiency, abrasion resistance and wet grip performance can beenhanced. Silica is not limited particularly, and silica generally usedin the rubber industry such as silica prepared by a dry method(anhydrous silica) and silica prepared by a wet method (hydrous silica)can be used. In particular, hydrous silica prepared by a wet method ispreferred for the reason that many silanol groups are contained. Silicamay be used alone or may be used in combination of two or more thereof.

A nitrogen adsorption specific surface area (N₂SA) of silica ispreferably not less than 20 m²/g, more preferably not less than 30 m²/g,further preferably not less than 100 m²/g. On the other hand, the N₂SAis preferably not more than 400 m²/g, more preferably not more than 300m²/g, further preferably not more than 280 m²/g. When the N₂SA is withinthe above-mentioned range, there is a tendency that fuel efficiency andprocessability are obtained in good balance. Herein, the N₂SA of silicais a value measured by a BET method in accordance with ASTM D3037-81.

The content of silica is preferably not less than 20 parts by mass, morepreferably not less than 30 parts by mass, further preferably not lessthan 40 parts by mass based on 100 parts by mass of the rubbercomponent. When the content of silica is not less than 20 parts by mass,there is a tendency that an effect of enhancing fuel efficiency andabrasion resistance by compounding silica is obtained satisfactorily.The content of silica is preferably not more than 120 parts by mass,more preferably not more than 110 parts by mass, further preferably notmore than 100 parts by mass based on 100 parts by mass of the rubbercomponent. When the content of silica is not more than 120 parts bymass, there is a tendency that lowering of dispersion of silica into therubber is inhibited, more satisfactory fuel efficiency, processabilityand abrasion resistance are obtained.

In addition to the above-mentioned components, the rubber compositionfor tire according to the present disclosure can comprise compoundingagents conventionally used in the rubber industry, for example, areinforcing filler other than silica, a processing aid, zinc oxide,stearic acid, various anti-aging agents, a softening agent such as anadhesive resin, oils, wax, a vulcanizing agent such as sulfur, variousvulcanization accelerators, and the like optionally according tonecessity.

Any of various reinforcing agents other than silica such as carbonblack, calcium carbonate, alumina, clay and talc which have been usuallyused for rubber compositions for a tire can be compounded, and from theviewpoint of excellent reinforcing property and abrasion resistance,carbon black is preferred.

Carbon black is not limited particularly, and those which are generallyused in the tire industry such as GPF, FEF, HAF, ISAF and SAF can beused, and fine particles carbon black produced and sold by MitsubishiChemical Corporation can be used preferably. These may be used alone ormay be used in combination of two or more thereof.

A nitrogen adsorption specific surface area (N₂SA) of carbon black ispreferably not less than 50 m²/g, more preferably not less than 80 m²/gfrom the viewpoint of weather resistance and reinforcing property.Further, the N₂SA of carbon black is preferably not more than 250 m²/g,more preferably not more than 220 m²/g from the viewpoint of fuelefficiency, dispersivity thereof, breaking resistance and durability.Herein, the N₂SA of carbon black is a value measured according to JIS K6217 Method A.

When carbon black is compounded, the content thereof is preferably notless than 3 parts by mass, more preferably not less than 5 parts by massbased on 100 parts by mass of the rubber component, from the viewpointof weather resistance. Further, the content of carbon black ispreferably not more than 40 parts by mass, more preferably not more than30 parts by mass from the viewpoint of fuel efficiency andprocessability.

Examples of the processing aid include fatty acid metal salt, fatty acidamide, amide ester, silica surfactant, fatty acid ester, a mixture offatty acid metal salt and amide ester, a mixture of fatty acid metalsalt and fatty acid amide, and the like. These may be used alone or maybe used in combination of two or more thereof. Among these, fatty acidmetal salt, amide ester, a mixture of fatty acid metal salt and amideester or fatty acid amide are preferred, and a mixture of fatty acidmetal salt and fatty acid amide is particularly preferred.

A fatty acid constituting the fatty acid metal salt is not limitedparticularly, and there are saturated or unsaturated fatty acids(preferably saturated or unsaturated fatty acids having 6 to 28 carbonatoms (more preferably 10 to 25 carbon atoms, further preferably 14 to20 carbon atoms)). Examples thereof include lauric acid, myristic acid,palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid,arachidic acid, behenic acid, nervonic acid, and the like. These may beused alone or may be used in combination of two or more thereof. Amongthese, saturated fatty acids are preferred, and saturated fatty acidshaving 14 to 20 carbon atoms are more preferred.

Examples of metal constituting the fatty acid metal salt include alkalimetals such as potassium and sodium, alkali earth metals such asmagnesium, calcium and barium, zinc, nickel, molybdenum, and the like.Among these, zinc and calcium are preferred, and zinc is more preferred.

Either saturated fatty acid amide or unsaturated fatty acid amide may beused as the fatty acid amide. Examples of saturated fatty acid amideinclude N-(1-oxooctadecyl)sarcosine, stearamide, behenamide, and thelike. Examples of unsaturated fatty acid amide include oleamide,cis-13-docosenoamide, and the like.

Examples of a mixture of fatty acid metal salt and fatty acid amideinclude Struktol WB16 which is a mixture of fatty acid calcium and fattyacid amide and is available from Struktol AG, and the like. Further,examples of fatty acid zinc salt include Ultra-Flow440 available fromPerformance Additives, and the like.

When a processing aid is compounded, the content thereof is preferablynot less than 0.8 part by mass, more preferably not less than 1.5 partsby mass based on 100 parts by mass of the rubber component. When thecontent is less than 0.8 part by mass, a satisfactory effect of addingthe processing aid may not be obtained. On the other hand, the contentis preferably not more than 10 parts by mass, more preferably not morethan 8 parts by mass, further preferably not more than 6 parts by mass.When the content exceeds 10 parts by mass, sliding between the polymerphases arises, and a polymer structure in which polymer phases areentangled with each other is difficult to obtain. Thus, abrasionresistance and breaking strength tend to be lowered.

There are, as an adhesion-imparting resin, resins such as aromaticpetroleum resins which have been used commonly for rubber compositionsfor tire. Examples of aromatic petroleum resins include a phenolicresin, a coumarone-indene resin, a terpene resin, a styrene resin, anacrylic resin, a rosin resin, a dicyclopentadiene resin (DCPD resin),and the like. Examples of the phenolic resin include Koreshin(manufactured by BASF), TACKIROL (manufactured by Taoka Chemical Co.,Ltd.), and the like. Examples of the coumarone-indene resin includeCOUMARONE (manufactured by NITTO CHEMICAL CO., LTD.), Esukuron(manufactured by Nippon Steel Chemical Co., Ltd.), Neo polymer(manufactured by Nippon Petrochemicals Co., Ltd.), and the like.Examples of the styrene resin include Sylvatraxx 4401 (manufactured byArizona Chemical), and the like. Examples of the terpene resin includeTR7125 (manufactured by Arizona Chemical), TO125 (manufactured byYasuhara Chemical Co., Ltd.), and the like.

A softening point of the adhesion-imparting resin is preferably notlower than 40° C., more preferably not lower than 60° C. When thesoftening point is not lower than 40° C., sufficient grip performancetends to be obtained. On the other hand, the softening point ispreferably not higher than 120° C., more preferably not higher than 100°C. When the softening point is not higher than 120° C., sufficient gripperformance tends to be obtained. In the present disclosure, thesoftening point of the resin is one specified in JIS K6220-1: 2001 andis a temperature at the time when the ball has dropped on a bottom platein the measurement with the ring and ball softening point measuringdevice.

A content of the adhesion-imparting resin is preferably not less than 3parts by mass, more preferably not less than 5 parts by mass based on100 parts by mass of the rubber component. When the content is not lessthan 3 parts by mass, sufficient grip performance tends to be obtained.On the other hand, the content of the adhesion-imparting resin ispreferably not more than 30 parts by mass, more preferably not more than25 parts by mass. When the content is not more than 30 parts by mass,sufficient abrasion resistance tends to be obtained, and good fuelefficiency tends to be obtained.

For zinc oxide, stearic acid, various anti-aging agents, oils and wax,those which have been used in the rubber industry can be used.

The vulcanizing agent is not limited particularly, and those which aregenerally used in rubber industries can be used, and those containingsulfur atoms are preferable. Examples thereof include powdered sulfur,precipitated sulfur, colloidal sulfur, surface-treated sulfur, insolublesulfur, and the like.

The vulcanization accelerator is not limited particularly, and examplesthereof include sulfenamide-, thiazole-, thiuram-, thiourea-,guanidine-, dithiocarbamate-, aldehyde amine- or aldehyde ammonia-,imidazoline- and xanthate-based vulcanization accelerators. Among these,sulfenamide-, thiuram- and guanidine-based vulcanization acceleratorsare preferred from a point that the effect of the present disclosure canbe obtained more suitably.

Examples of sulfenamide-based vulcanization accelerators include CBS(N-cyclohexyl-2-benzothiazolylsulfenamide), TBBS(N-t-butyl-2-benzothiazolylsulfenamide),N-oxyethylene-2-benzothiazolylsulfenamide,N,N′-diisopropyl-2-benzothiazolylsulfenamide,N,N-dicyclohexyl-2-benzothiazolylsulfenamide, and the like. Examples ofthiazole-based vulcanization accelerators include2-mercaptobenzothiazole, dibenzothiazolyldisulfide, and the like.Examples of thiuram-based vulcanization accelerators includetetramethylthiuram monosulfide, tetramethylthiuram disulfide,tetrabenzylthiuram disulfide (TBzTD), and the like. Examples ofguanidine-based vulcanization accelerators include diphenylguanidine(DPG), di-o-tolylguanidine, o-tolylbiguanidine, and the like. These maybe used alone or may be used in combination of two or more thereof.Among these, TBBS, TBzTD and DPG are preferred, and combination use ofthese three vulcanization accelerators is more preferred from a pointthat the effect of the present disclosure can be obtained suitably.

As mentioned above, in the method of preparing a rubber composition fora tire of the present disclosure, as far as the rubber component and theabove-mentioned compound of the formula (1) are kneaded before kneadingthe silane coupling agent having a mercapto group with the rubbercomponent, the preparation method is not limited particularly. Forexample, the preparation method can be carried out by kneading therubber component and the compound of the formula (1) in an X-kneadingstep (a step X) and thereafter kneading, in a Y-kneading step (a stepY), the silane coupling agent having a mercapto group with the kneadedproduct obtained in the step X. Alternatively in the step X, the rubbercomponent and the compound of the formula (1) may be kneaded for a givenperiod of time (a step X1), and thereafter, without discharging thekneaded product, the silane coupling agent having a mercapto group maybe added, followed by further kneading.

In the step X, silica can be further kneaded. While a timing of addingsilica in the step X is not limited particularly, in the case of addingchemicals dividedly in the step X, it is preferable to add silica afteraddition of the compound of the formula (1). Further, in the case ofcharging the silane coupling agent having a mercapto group in the stepX, silica may be added simultaneously with the addition of the silanecoupling agent having a mercapto group, or it is more preferable to addsilica earlier than the addition of the silane coupling agent having amercapto group.

Furthermore, kneading of silica with the rubber component may beconducted in any of steps except an F-kneading step (a step F) where avulcanizing agent is kneaded, and it is preferable that by dividing thetotal amount of silica, the divided amounts of silica are kneaded in therespective steps.

As far as the silane coupling agent having a mercapto group is kneadedwith the rubber component after the kneading of the compound of theformula (1), the kneading of the silane coupling agent can be performeddividedly in the respective kneading steps.

In one embodiment of the method of preparing a rubber composition for atire of the present disclosure, a kneaded product X is obtained, forexample, by kneading the rubber component and the compound representedby the formula (1) (step X1); adding and kneading the reinforcing agentssuch as carbon black and silica (step X2); and further adding andkneading the silane coupling agent having a mercapto group (step X3),followed by discharging. Thereafter, silica and the silane couplingagent having a mercapto group are added to the kneaded product X,followed by kneading (step Y) and then discharging to obtain a kneadedproduct Y. Next, silica and the silane coupling agent having a mercaptogroup are added to the kneaded product Y, followed by kneading (step Z)and then discharging to obtain a kneaded product Z. Then an unvulcanizedrubber composition can be obtained by adding the vulcanizing agent andthe vulcanization accelerator to the obtained kneaded product Z andsubjecting the mixture to kneading (step F).

It is preferable that the kneading in the step X is performed at adischarge temperature of 140° C. to 170° C. for 1 to 5 minutes. It ispreferable that the kneaded product obtained in the step X is used forthe following steps after having been cooled to a temperature of usuallynot higher than 80° C., preferably 25° C. to 45° C.

It is preferable that the kneading in the step Y is performed at adischarge temperature of 130° C. to 160° C. for 1 to 5 minutes. It ispreferable that the kneaded product obtained in the step Y is used forthe following steps after having been cooled to a temperature of usuallynot higher than 80° C., preferably 25° C. to 45° C.

It is preferable that the kneading in the step Z is performed at adischarge temperature of 130° C. to 160° C. for 1 to 5 minutes. It ispreferable that the kneaded product obtained in the step Z is used forthe following steps after having been cooled to a temperature of usuallynot higher than 80° C., preferably 25° C. to 45° C.

It is preferable that the kneading in the step F is performed at adischarge temperature of 90° C. to 130° C. for 1 to 5 minutes.

For each of the kneading steps in the method of preparing a rubbercomposition for a tire of the present disclosure, known kneadingequipment can be used, and there are, for example, a Banbury mixer, akneader, an open roll, and the like which perform kneading and mixing byapplying a mechanical shearing force to a material to be kneaded.

The rubber composition for tire of the present disclosure is a rubbercomposition for tire which comprises the rubber component, the silanecoupling agent having a mercapto group and the compound represented bythe formula (1), is prepared by kneading the silane coupling agenthaving a mercapto group with the rubber component subjected to kneadingwith the compound represented by the formula (1), and has improvedprocessability. The reason therefor is considered to be such that asmentioned above, the compound represented by the formula (1) and kneadedwith the rubber component forms —S—S— bond with the mercapto group ofthe added silane coupling agent having a mercapto group, therebypreventing gelation of the rubber component attributable to the silanecoupling agent.

The rubber composition for a tire of the present disclosure can be usedon each of tire members such as tread, under tread, carcass, side walland bead. In particular, a tire having a tread formed from the rubbercomposition of the present disclosure is preferable since it hasexcellent abrasion resistance.

The method of producing a tire of the present disclosure is a method ofproducing a tire comprising a forming step of subjecting theunvulcanized rubber composition prepared by the preparation method ofthe present disclosure to extrusion processing to a shape of a member ofa tire such as a tread and then forming together with other tire memberson a tire building machine by a usual forming method, thus forming anunvulcanized tire, and a vulcanizing step of heating and compressingthis unvulcanized tire in a vulcanizer. A vulcanization temperature is,for example, not lower than 120° C. and not higher than 200° C. It doesnot matter whether the tire according to the present disclosure is usedon a pneumatic tire or a non-pneumatic tire. Examples of a pneumatictire include tires for passenger cars, tires for trucks and buses, tiresfor two-wheeled vehicles, high performance tires, and the like. Herein,high performance tires mean tires particularly being excellent in gripperformance, and is a concept encompassing tires used on racing cars.

EXAMPLE

The present disclosure is explained by means of Examples, but is notlimited to the Examples.

Various chemicals used in Examples and Comparative examples arecollectively shown below.

SBR: SLR6430 available from TRINSEO S.A. (S-SBR, styrene content: 40% bymass, an amount of vinyl bond: 18 mole %, an oil-extended rubbercontaining 37.5 parts by mass of oil to 100 parts by mass of rubbercomponent)BR: BR150B manufactured by Ube Industries, Ltd., (cis-1,4 content: 97%)Compound of the formula (1): TP-50 manufactured by Rhein Chemie(compound represented by the formula (1), R¹ to R⁴: n-butyl, content ofactive ingredient: 50% by mass)Fine particles carbon black: Carbon black having a nitrogen adsorptionspecific surface area (N₂SA) of 180 m²/gSilica: ULTRASIL (registered trademark) VN3 available from EvonikDegussa GmbH (N₂SA: 175 m²/g)Silane coupling agent A: NXT-Z45 available from Momentive PerformanceMaterials Inc. (a copolymer of a bonding unit A and a bonding unit B(bonding unit A: 55 mole %, bonding unit B: 45 mole %))Silane coupling agent B: Si363 manufactured by Evonik Degussa GmbHZinc oxide: ZINC FLOWER No. 1 available from Mitsui Mining & SmeltingCo., Ltd.Stearic acid: Stearic acid “Tsubaki” available from NOF CORPORATION Wax:OZOACE 0355 manufactured by Nippon Seiro Co., Ltd. (paraffin) Oil:VivaTec400 (TDAE oil) manufactured by H&R Co., Ltd.Styrene resin: SylvaTraxx (registered trademark) 4401 available fromArizona Chemical (softening point: 85° C.)Anti-aging agent (1): Antigen 6C(N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine) available fromSumitomo Chemical Company, LimitedAnti-aging agent (2): Nocrac 224 (TMQ, Polymerized2,2,4-trimethyl-1,2-dihydroquinoline) manufactured by OUCHI SHINKOCHEMICAL INDUSTRIAL CO., LTD.Processing aid (1): Ultra-Flow (registered trademark) 440 available fromPerformance Additives (natural fatty acid zinc/metal soap)Processing aid (2): Struktol WB16 available from Schill & SeilacherStruktol GmbH (a mixture of fatty acid ester and fatty acid metal salt)Sulfur: HK-200-5 available from Hosoi Chemical Industry Co., Ltd.(powdered sulfur containing 5% oil)Vulcanization accelerator (1): SANCELER NS-G(N-tert-butyl-2-benzothiazole sulfenamide (TBBS)) manufactured bySANSHIN CHEMICAL INDUSTRY CO., LTD.Vulcanization accelerator (2): SANCELER TBZTD (tetrabenzylthiuramdisulfide (TBzTD)) manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.Vulcanization accelerator (3): Nocceler D (N,N′-diphenylguanidine)manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD.

Examples 1 to 7 and Comparative Examples 1 to 6

According to the formulations shown in Table 1, various chemicals shownin the step X1 were kneaded for 20 seconds with a 1.7 liter Banburymixer. Thereafter, various chemicals shown in the step X2 of Table 1were added, followed by kneading for 80 seconds. Then various chemicalsshown in the step X3 of Table 1 were added, followed by kneading for 80seconds, and a kneaded product was discharged at a discharge temperatureof 160° C. The obtained kneaded products were cooled to about 30° C. tobe used in the following step.

Next, to the obtained kneaded products were added other variouschemicals according to the formulations shown in the step Y of Table 1,followed by kneading for two minutes at a discharge temperature of 150°C. The obtained kneaded products were cooled to about 30° C. to be usedin the following step. Thereafter, to the kneaded products obtained inthe step Y were added other various chemicals according to theformulations shown in the step Z of Table 1, followed by kneading fortwo minutes at a discharge temperature of 145° C. The obtained kneadedproducts were cooled to about 30° C. to be used in the following step.To the kneaded products obtained in the step Z were added sulfur andvulcanization accelerators according to the formulations shown in thestep F of Table 1, followed by kneading for three minutes under adischarge temperature of 125° C. with an open roll to obtainunvulcanized rubber compositions.

Each of the obtained unvulcanized rubber compositions were subjected topress vulcanization for 12 minutes at 170° C. with a metal mold having athickness of 2 mm to obtain vulcanized rubber compositions.

Further, the obtained unvulcanized rubber compositions were formed intoa shape of a tread and laminated together with other tire members toform unvulcanized tires which were then subjected to vulcanization for15 minutes at 165° C. to produce tires (tire size: 205/55R16).

Examples 8 and 9 and Comparative Examples 7 to 11

Unvulcanized rubber compositions, vulcanized rubber compositions andtires were produced according to the formulations shown in Table 2 inthe same manner as in Example 1 except that the addition of chemicals inthe step X was not carried out stepwise.

Processability of the unvulcanized rubber compositions obtained inExamples 1 to 9 and Comparative Examples 1 to 11 were evaluated by thefollowing test. The results are shown in Tables 1 and 2.

<Processability (Average Surface Roughness Ra)>

One kg of an unvulcanized rubber composition was wound in a width of 30cm and a thickness of 2 mm on an 8-inch open roll and was subjected tokneading until a rubber temperature reaches 95±+5° C. to obtain a rubbersheet. Then the obtained rubber sheet was cut and a surface roughness ofa rubber compound was measured with a surface roughness meter based onarithmetic mean roughness Ra of JIS B0601. The obtained results areexpressed as an index by the following formula using Comparative Example1 as a reference comparative example for Examples 1 to 6 and 8 andComparative Examples 2 to 4 and 7 to 9, and using Comparative Example 5as a reference comparative example for Examples 7 and 9 and ComparativeExamples 6, 10 and 11.

(Processability index)=100×Surface roughness Ra of Reference ComparativeExample/Surface roughness Ra of Each Example

TABLE 1 Compounding amount Example Comparative Example (part by mass) 12 3 4 5 6 7 1 2 3 4 5 6 Step X Step X1 SBR 110 110 110 110 110 110 82.5110 110 110 110 82.5 82.5 BR 20 20 20 20 20 20 40 20 20 20 20 40 40Compound of the formula (1): 2 0.5 1 3 2 2 2 — — — — — — TP-50 Step X2Carbon black 5 5 5 5 5 5 5 5 5 5 5 5 5 Silica 55 55 55 55 55 55 55 55 5555 55 55 55 Wax 2 2 2 2 2 2 2 2 2 2 2 2 2 Processing aid (1) 2 2 2 2 2 22 2 2 2 2 2 2 Step X3 Silica 10 10 10 10 10 10 10 10 10 10 10 10 10Silane coupling agent A 5 5 5 5 — — 5 5 5 5 — 5 5 Silane coupling agentB — — — — — 5 — — — — 5 — — Compound of the formula (1): — — — — — — — —2 — 2 — 2 TP-50 Oil 5 5 5 5 5 5 5 5 5 5 5 5 5 Step Y Silica 25 25 25 2525 25 25 25 25 25 25 25 25 Silane coupling agent A 2 2 2 2 7 — 2 2 2 2 —2 2 Silane coupling agent B — — — — — 2 — — — — 2 — — Compound of theformula (1): — — — — — — — — — 2 — — — TP-50 Styrene resin 10 10 10 1010 10 10 10 10 10 10 10 10 Stearic acid 3 3 3 3 3 3 3 3 3 3 3 3 3 Oil 33 3 3 3 3 3 3 3 3 3 3 3 Step Z Silica 10 10 10 10 10 10 10 10 10 10 1010 10 Silane coupling agent A 1 1 1 1 1 — 1 1 1 1 — 1 1 Silane couplingagent B — — — — — 1 — — — — 1 — — Processing aid (2) 3 3 3 3 3 3 3 3 3 33 3 3 Oil 3 3 3 3 3 3 3 3 3 3 3 3 3 Step F Sulfur 1.5 1.5 1.5 1.5 1.51.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization accelerator (1) 2 2 2 2 22 2 2 2 2 2 2 2 Vulcanization accelerator (2) 0.5 0.5 0.5 0.5 0.5 0.50.5 0.5 0.5 0.5 0.5 0.5 0.5 Vulcanization accelerator (3) 2 2 2 2 2 2 22 2 2 2 2 2 Zinc oxide 2 2 2 2 2 2 2 2 2 2 2 2 2 Anti-aging agent (1) 33 3 3 3 3 3 3 3 3 3 3 3 Anti-aging agent (2) 1 1 1 1 1 1 1 1 1 1 1 1 1Evaluation Processability index 117 115 118 120 125 116 116 100 105 102105 100 104 (Surface roughness Ra)

TABLE 2 Compounding amount Example Comparative Example (part by mass) 89 7 8 9 10 11 Step X SBR 110 82.5 110 110 110 82.5 82.5 BR 20 40 20 2020 40 40 Compound of the formula (1): 2 2 — 2 — — 2 TP-50 Carbon black 55 5 5 5 5 5 Silica 65 65 65 65 65 65 65 Silane coupling agent A — — 5 55 5 5 Silane coupling agent B — — — — — — — Wax 2 2 2 2 2 2 2 Processingaid (1) 2 2 2 2 2 2 2 Oil 5 5 5 5 5 5 5 Step Y Silica 25 25 25 25 25 2525 Silane coupling agent A 7 7 2 2 2 2 2 Silane coupling agent B — — — —— — — Compound of the formula (1): — — — — 2 — — TP-50 Styrene resin 1010 10 10 10 10 10 Stearic acid 3 3 3 3 3 3 3 Oil 3 3 3 3 3 3 3 Step ZSilica 10 10 10 10 10 10 10 Silane coupling agent A 1 1 1 1 1 1 1 Silanecoupling agent B — — — — — — — Processing aid (2) 3 3 3 3 3 3 3 Oil 3 33 3 3 3 3 Step F Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanizationaccelerator (1) 2 2 2 2 2 2 2 Vulcanization accelerator (2) 0.5 0.5 0.50.5 0.5 0.5 0.5 Vulcanization accelerator (3) 2 2 2 2 2 2 2 Zinc oxide 22 2 2 2 2 2 Anti-aging agent (1) 3 3 3 3 3 3 3 Anti-aging agent (2) 1 11 1 1 1 1 Evaluation Processability index 123 122 100 105 102 100 104(Surface roughness Ra)

From the results shown in Tables 1 and 2, it can be seen that inComparative Examples 1 and 5, where a silane coupling agent having amercapto group was used but a compound of the formula (1) was not used,processability was not good, and that in Comparative Examples 2, 4 and6, where a compound of the formula (1) was kneaded at the same time asin the kneading of the silane coupling agent having a mercapto group,processability was improved as compared to those of Comparative Examples1 and 5 but was not sufficient. It can be seen that in any of Examples 1to 9, where a compound of the formula (1) was kneaded with a rubbercomponent before kneading a silane coupling agent having a mercaptogroup with a rubber component, processability was enhanced remarkably.

What is claimed is:
 1. A method of preparing a rubber composition for atire comprising initiating kneading of a rubber component and a compoundrepresented by the following formula (1) before kneading the rubbercomponent and a silane coupling agent having a mercapto group:

wherein each of R¹ to R⁴ independently represents a straight-chain orbranched chain alkyl group having 1 to 18 carbon atoms or a cycloalkylgroup having 5 to 12 carbon atoms.
 2. The preparation method of claim 1,wherein the rubber component comprises not less than 50% by mass of adiene rubber having a styrene content of 25 to 50% by mass and an amountof a vinyl bond of 10 to 35 mole %.
 3. The preparation method of claim2, wherein the styrene content is not less than 2 times the amount of avinyl bond.
 4. The preparation method of claim 1, wherein the silanecoupling agent having a mercapto group is a compound represented by thefollowing formula (2) and/or a compound comprising a bonding unit Arepresented by the following formula (3) and a bonding unit Brepresented by the following formula (4):

wherein R¹⁰¹ to R¹⁰³ represent a straight-chain or branched chain alkylgroup having 1 to 12 carbon atoms, a straight-chain or branched chainalkoxy group having 1 to 12 carbon atoms, or a group represented by—O—(R¹¹¹—O)_(z)—R¹¹² (z R¹¹¹s represent straight-chain or branched chaindivalent hydrocarbon groups having 1 to 30 carbon atoms, z R¹¹¹s may bethe same or different, R¹¹² represents a straight-chain or branchedchain alkyl group having 1 to 30 carbon atoms, a straight-chain orbranched chain alkenyl group having 2 to 30 carbon atoms, an aryl grouphaving 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbonatoms, z represents an integer of 1 to 30), R¹⁰¹ to R¹⁰³ may be the sameor different, and R¹⁰⁴ represents a straight-chain or branched chainalkylene group having 1 to 6 carbon atoms,

wherein x is an integer of 0 or more, y is an integer of 1 or more, R²⁰¹represents a hydrogen atom, a halogen atom, a straight-chain or branchedchain alkyl group having 1 to 30 carbon atoms, a straight-chain orbranched chain alkenyl group having 2 to 30 carbon atoms, astraight-chain or branched chain alkynyl group having 2 to 30 carbonatoms, or the alkyl group in which a terminal hydrogen atom has beenreplaced with a hydroxyl group or a carboxyl group, R²⁰² represents astraight-chain or branched chain alkylene group having 1 to 30 carbonatoms, a straight-chain or branched chain alkenylene group having 2 to30 carbon atoms, or a straight-chain or branched chain alkynylene grouphaving 2 to 30 carbon atoms, and a ring structure may be formed withR²⁰¹ and R²⁰².
 5. A method of producing a tire comprising a step offorming a tire member from the rubber composition for tire obtained bythe preparation method of claim 1 and forming a green tire by combiningthe tire member with other tire members, and a vulcanization step ofvulcanizing the green tire obtained in the forming step.
 6. A rubbercomposition for a tire comprising a rubber component, a silane couplingagent having a mercapto group and a compound represented by thefollowing formula (1), which is prepared by kneading the silane couplingagent having a mercapto group with the rubber component with which thecompound represented by the following formula (1) is kneaded:

wherein each of R¹ to R⁴ independently represents a straight-chain orbranched chain alkyl group having 1 to 18 carbon atoms or a cycloalkylgroup having 5 to 12 carbon atoms.